Fungal Infections
Fungus Among Us
By Amy J. Spaeth, DVM
This article has been written in the memory of Jojos Sooo What, "Sydney",
who lost her life to Blastomycosis in January of 2005.
We have all heard of Ringworm or have had one of our dogs diagnosed with an ear infection caused by yeast. These are types of cutaneous or skin fungal infections. On the other hand, there are systemic or body fungal infections that invade any organ system of the body. Humans and dogs alike can acquire these systemic fungal infections. This article was written to raise your awareness about four of major systemic fungal infections of dogs: blastomycosis, coccidioidomycosis, histoplasmosis, and cryptococcosis.
Blastomycosis
Blastomycosis (Blasto) is a systemic fungal infection caused by the soil organism Blastomyces dermatitidis. In nature, Blasto grows in the fungal or mold form, that produces thousands of infective microscopic spores. Once airborne, these spores can be inhaled and settle into the deep portions of the lungs. In the body, these spores are transformed into the yeast form. Dogs and people are most commonly infected with blastomycosis, but it has also been reported in cats, horses, wolves, ferrets and polar bears.
The mold form of Blasto grows in sandy, acidic soil, that is in close proximity to water. Rain or heavy dew appears to facilitate the release of infectious spores. Access to sites that have been excavated, thus exposing the organisms that are deep in the soil, also increase the risk for infection. It may even be found in landscaping or potting soil. Blastomycosis has a well-defined endemic distribution that includes the Mississippi, Missouri, and Ohio River Valleys, the Great Lakes region, the mid-Atlantic states, the along the eastern seaboard. Sporting or hunting dogs appear to be at greater risk of contracting Blasto, since they are more commonly exposed to soil in wet areas. Infection is more commonly seen in dogs ages 1- 4 years. For unknown reasons, male dogs are more likely to contract Blasto than females.
When in the soil, the mold form of Blasto releases thousands of microscopic spores that are cast away in the dust or dirt which is stirred up when the soil is disturbed. The spores are inhaled and settle deep in the lungs or alveolar sacs. Here they become infective yeast-like organisms and quickly multiply. Once inhaled into the lungs, it can be a few days to several weeks (2-14 weeks) before any signs of disease appear. Blastomycosis can also spread throughout the body from the lungs, invading the lymph nodes, eyes, brain, joints and bones, prostate and testicles, and skin. Clinical signs include: fever (103 F or higher), anorexia, weight loss, coughing, difficulty breathing, lameness, enlarged lymph nodes, eye disease (blindness), testicular and prostatic enlargement, or skin lesions that drain blood or pus.
Diagnosis should be made by identification of the organism in tissue or fluid samples. Transtracheal washes, lung aspirates, lymph nodes aspirates, impression smears of draining skin lesions, and histological examination of a removed blind eye will yield organisms. A chest X-ray and complete blood work are important but are not diagnostic themselves.
The treatment of choice for blastomycosis is oral antifungal medication including itraconazole (Sporanox) or fluconazole (Diflucan). These tablets are administered twice a day at first, then once daily for four to six months. The side effects of these drugs are related to liver toxicity, including anorexia, vomiting and nausea. The biggest draw back is in the cost, which is about $5-10 a day for a 50 pound dog. For many years Amphotericin B was used to treat blastomycosis, but is not routinely used today, due to its potential of causing kidney failure. It is still the best choice however for acute, life- threatening illness. It is given as an intravenous injection over several hours, every other day for a week, followed by oral antifungal medication for 4-6 months. About 75% of dogs diagnosed with blastomycosis survive. Death usually results form respiratory failure, that occurs during the first 7 days of treatment. This has been attributed to the inflammatory response to the death of the organism in the lungs. Most dogs diagnosed with Blasto are euthanized due to the cost of treatment. When Blasto effects the eye, vision is usually lost and the eye is usually removed because it does not respond well to treatment. Approximately 20% of dogs will relapse within three to six months after completion of treatment. A second course of itraconazole cures most dogs.
Blastomycosis is not contagious to other pets or family members. Spores from the soil must be inhaled to result in disease.
Coccidioidomycosis
Coccidioidomycosis, or more commonly known as "Valley Fever", is a systemic fungal infection caused by the organism, Coccidioides immitis. Like Blasto, coccidioidomycosis exists in nature as a mold which produce arthroconidia (which are like spores). These arthroconidia are inhaled into the lungs where they change into round spherules (like the yeast form of Blasto).
The mold form of coccidioidomycosis exist in an arid climate, with alkaline soil, hot summers and low annual rainfall. It grows several inches deep into the soil, where it can survive the high temperature and low moisture. After a period of rainfall, the organism returns to the soil surface, where it releases large numbers of arthroconidia which are spread by the wind. Outbreaks of this disease usually occur following dust storms, earthquakes, following the rainy season, and excavation of the soil. Endemic areas include areas of southern Arizona, central California, southern New Mexico, and west Texas. There is no breed or sex predilection for this disease, but most patients are young animals under the age of 4 years.
Once the arthroconidia are inhaled into the lungs, signs of the disease appear within 1-3 weeks. Coccidioidomycosis commonly spreads from the lungs to other parts of the body, including bones, eyes, heart, testicles, skin, brain, spinal cord, and spleen, liver or kidney. Clinical signs include: dry, harsh cough, fever, anorexia, weight loss, weakness, lameness, seizures, ataxia, draining skin lesions, and blindness.
Definitive diagnosis is made by identifying the organism in a lesion or tissue biopsy. Aspirates of lymph nodes and impression smears of draining lesions may, in some patients, yield identification of the organism. Usually complete blood counts, blood chemistry panels, and urinalysis show only nonspecific changes. Radiographs (X-rays) of the lung and bones may show characteristic changes that are useful for diagnosis. When the organism cannot be found, antibody tests are commonly used as a presumptive test.
Treatment for coccidioidomycosis is with an antifungal medcation. The most commonly prescribed and least expensive antifungal is ketoconazole (Nizoral). It is given orally, with food, twice daily for six to twelve months. Side effects include nausea, vomiting, and loss of appetite. In some cases, itaconazole and fluconazole can be more effective in resolving clinical signs, but are extremely expensive.
The prognosis for coccidioidomycosis is guarded to grave. With treatment the overall recovery rate has been approximately 60 %. When confined to the lungs, the chances of a complete recovery are better then when the fungus has spread to other parts of the body. Some dogs can never be completely weaned from medication without relapsing. A small proportion of dogs die in spite of treatment.
Dogs with coccidioidomyosis should not be considered contagious to other pets or family members. The disease is only acquired through inhalation of the spore in desert soil.
Histoplasmosis
Histoplasmosis is a systemic fungal infection caused by the soil-borne organism, Histoplasma capsulatum. It is found in many temperate and subtropical regions of the world. In the United States it is endemic in the Mississippi and Ohio River Valleys and the Appalachian Mountain range. The fungus grows best in moist and humid conditions and in soil containing decomposing nitrogen-rich matter from bird, chicken or bat excrement.
The organism enters the body by inhaling the microconidia (spores) into the deep portions of the lung. In the lung the organism converts to the yeast form and spreads throughout the body, including the intestines, eye, skin, liver spleen, lymph nodes and bones. Infection may also be obtained by ingestion, which leads to intractable diarrhea and weight loss. Clinical signs of the lung form of histoplasmosis include: cough, difficulty breathing, fever, weight loss, and enlarged lymph nodes. If spreading has occurred there may be weeping , ulcerative sores of the skin, enlarged liver and spleen, depression, loss of appetite, lameness and eye disease. If ingestion of the organism has occurred or it has spread to the intestines, severe diarrhea, with fresh blood, mucous, a high fever, anemia and straining to defecate may be seen.
Definitive diagnosis of histoplasmosis requires identification of the organism in transtracheal washes, lung aspirates, rectal scrapings intestinal biopsy or liver and spleen biopsy. Radiographic findings are often highly suggestive of hisoplasmosis. Antibody detection provides a presumptive diagnosis.
Oral itraconazole is the treatment of choice and usually requires four to six months of therapy. Ketoconazole can also be used, but it is less effective and has more side effects.
Both humans and dogs are at risk of exposure to histoplasmosis. However, transmission from dog to dog or dog or human has not been reported.
Cryptococcosis
The organism, Cryptococcus neoformans, is found in many geographical regions. The infection is acquired from inhalation of the soil-borne organisms or in urban areas from inhalation of the air-borne organism from pigeon excrement. After inhalation, the organism may deposit in the upper respiratory tract or lodge deep in the lung. Signs of nasal involvement include: bloody nasal discharge, sneezing, or deformity of the overlying nasal bones. Once in the lung, the organism can spread to other parts of the body including the skin, CNS, and eyes. Skin lesions are usually characterized by ulcers that may involve the nose, tongue, gums, lips, nail beds or skin. CNS signs include head tilt, facial paralysis, ataxia, circling, seizure or blindness.
Definitive diagnosis is made by identification of the organism in sample of nose or skin exudate, cerebrospinal fluid, or impression smears of draining skin lesions. Blood work is often normal and nasal radiographs may show characteristic changes.
Treatment cryptococcosis is with oral itraconazole or fluconazole for six to ten months. Ketoconazole is not as effective and has more side effects.
Currently there is no vaccine available for any of these fungal infections. When your dog becomes ill, it is important that you give your veterinarian a detailed report of your dog's travel history for the past six months. Tell your vet what your dog's daily environment is like (i.e. swimming, hunting, digging holes in the yard, recently at the newly built house, eats the bird food under your wild bird feeder, etc.). A detailed account of your dog's life (lifestyle) is a key step in figuring out your dog's mystery illness.
